Twitter itself has the background. Some notable differences to Adwords are that the promoted tweets can be replied to and retweeted just like any other Tweet.

Also, interestingly, “according to Riyaad Minty, head of social media at Al Jazeera English, the @AJEnglish team is operating their Promoted Tweets campaign just like a news desk.” That’s because the content is the advertising, rather than the advertising driving users to the content.

Some metrics to come out of this, according to Twitter (they’re linking to evidence here):